Ethylene-vinyl ester saponified copolymers (hereinafter often referred to as “EVOH resins”) have exceedingly high intermolecular force due to hydrogen bonding between the hydroxyl groups present as side chains of the polymer. These copolymers hence have high crystallinity and have high intermolecular force even in the amorphous portions. Because of this, gas molecules and the like are less apt to pass through films employing EVOH resins, and the films employing EVOH resins show excellent gas barrier properties.
However, EVOH resins have a drawback in that the resins are hard and brittle and have poor flexibility. There have hence been problems, for example, in that in cases when EVOH resins are used as packaging materials or molding materials and bent repeatedly, the materials come to have cracks or pinholes due to flexing fatigue, etc. and be unable to retain the excellent performance.
As a means for overcoming the problem, a modified EVOH resin has been proposed, the modified EVOH resin being obtained by subjecting a lactone compound to a ring-opening polymerization reaction in the presence of an EVOH resin to thereby graft an aliphatic polyester to hydroxyl groups of the EVOH resin by ester bonds (see, for example, Patent Document 1).